Insulated gate silicon nanowire transistor and method of manufacture

ABSTRACT

An insulated gate silicon nanowire transistor amplifier structure is provided and includes a substrate formed of dielectric material. A patterned silicon material may be disposed on the substrate and includes at least first, second and third electrodes uniformly spaced on the substrate by first and second trenches. A first nanowire formed in the first trench operates to electrically couple the first and second electrodes. A second nanowire formed in the second trench operates to electrically couple the second and third electrodes. First drain and first source contacts may be respectively disposed on the first and second electrodes and a first gate contact may be disposed to be capacitively coupled to the first nanowire. Similarly, second drain and second source contacts may be respectively disposed on the second and third electrodes and a second gate contact may be disposed to be capacitively coupled to the second nanowire.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

FIELD OF THE INVENTION

The present invention relates generally to transistor structures and, more particularly, to an insulated gate silicon nanowire transistor structure.

BACKGROUND OF THE INVENTION

As is known, free-standing nanostructures are currently being extensively explored. These nanostructures are especially attractive for sensor applications because their high surface-to-volume ratio makes them very sensitive to charged species adsorbed on their surfaces. Lateral growth of carbon nanotubes between two electrodes during chemical vapour deposition (CVD) has been realized for which a lateral electric field applied between the electrodes attracts the growing nanotube towards the counter-electrode. Although the potential of carbon nanotubes for applications such as gas-sensing field-effect devices has been demonstrated, the difficulty of synthesizing only metallic or only semiconducting nanotubes and the difficulty of modifying nanotube surfaces have limited their development as nanosensors.

Lateral growth of GaAs nanowhiskers by metalorganic vapour phase epitaxy (MOVPE) from vertical ridges on a GaAs substrate using Au nanoparticles as the catalyst has also been demonstrated. However, the properties of the mechanical connection between a bridging nanowire and the vertical sidewall have not been favorable.

Nanowires made of silicon are especially attractive because of silicon's compatibility with existing IC processes. Moreover, the chemical and physical properties of silicon can be controlled to adjust the device sensitivity, and silicon nanowires can be selectively grown. Using silicon allows the vast knowledge of silicon technology to be applied to applications such as sensing. Using semiconductor nanowires, researchers have demonstrated electrical sensors for biological and chemical species, and designed a range of nanoelectronic and photonic devices in different material systems. In many of these demonstrations, nanowires were assembled after growth into parallel or crossed arrays by alignment aided by fluid flow or by applying electric fields. In other cases, electrical contacts were defined with electron-beam lithography on a few selected nanowires.

Although connecting electrodes to nanowires one at a time contributes to understanding the characteristics of nanowires and exploring novel device applications, it cannot be used for reproducible mass-fabrication of dense, low-cost device arrays. A massively parallel, self-assembly technique is needed to allow bridging of silicon nanowires between electrodes using only relatively coarse lithography principles.

It would, therefore, be desirable to overcome the aforesaid and other disadvantages.

SUMMARY OF THE INVENTION

In one aspect of the present invention, an insulated gate silicon nanowire transistor amplifier structure is set forth. The insulated gate silicon nanowire transistor amplifier structure includes a substrate formed of dielectric material. A patterned silicon material may be disposed on the substrate and has at least first, second and third electrodes uniformly spaced on the substrate by first and second trenches. A first nanowire may be formed in the first trench and is operative to electrically couple the first and second electrodes. Similarly, a second nanowire may be formed in the second trench and is operative to electrically couple the second and third electrodes. First drain and first source contacts may be respectively disposed on the first and second electrodes. Further, a first gate contact is disposed to be capacitively coupled to the first nanowire.

The transistor amplifier structure further includes second drain and second source contacts, which are respectively disposed on the second and third electrodes. A second gate contact is also disposed to be capacitively coupled to the second nanowire. In this arrangement, the first drain contact is coupled to receive current from a first source and the second gate contact is coupled to receive current from a second source for generating an electric field sufficient to permit current from the first source to flow through the first and second nanowires and simultaneously providing an amplified output realized between the first gate and first source contacts.

In another aspect of the present invention, a method of forming an insulated gate silicon nanowire transistor amplifier structure is set forth. The method includes disposing a silicon layer on a dielectric substrate and patterning the silicon layer for forming at least first, second and third electrodes separated by first and second trenches. A first nanowire may be grown laterally in the first trench for electrically coupling the first and second electrodes. Similarly, a second nanowire may be grown laterally in the second trench for electrically coupling the second and third electrodes. The first and second nanowires may thereafter be encapsulated in a first dielectric material.

The method further includes disposing first drain and first source contacts on respective first and second electrodes. Similarly, the second drain and second source contacts may be disposed on respective second and third electrodes. A first gate contact may be disposed on the first dielectric material in close proximity to the first nanowire and a second gate contact may be disposed on the first dielectric material in close proximity to the second nanowire. In this arrangement, the first drain, source and gate contacts serve as an interface to a first transistor stage of the transistor amplifier structure and the second drain, source and gate contacts serve as an interface to a second transistor stage of the transistor amplifier structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows an embodiment of the insulated gate silicon nanowire transistor amplifier structure in accordance with the present invention;

FIGS. 2 a-2 f show a process of forming one or more nanowires in a first trench located on a first transistor stage of the insulated gate silicon nanowire transistor amplifier structure of FIG. 1 and exemplary images of the one or more nanowires; and

FIGS. 3 a-3 e show one embodiment of a method of forming a first transistor stage of the insulated gate silicon nanowire transistor amplifier structure of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an insulated gate silicon nanowire transistor amplifier structure and method of manufacturing the same. The insulated gate silicon nanowire transistor amplifier structure is constructed and arranged to permit operation in the THz range by ballistically transporting electrons through a number of nanowires located within the transistor structure, as will be described in further detail below.

Referring now to FIG. 1, shown is one embodiment of the insulated gate silicon nanowire transistor amplifier structure 10 in accordance with principles of the present invention. In the illustrative embodiment, the insulated gate silicon nanowire transistor amplifier structure 10 includes a substrate 12. In an embodiment, the substrate 12 can be formed of silicon oxide, sapphire, glass or other sturdy dielectric materials or a layer of such materials deposited on a silicon substrate. A silicon layer 14 may be disposed on the substrate 12, which wafer 14 may be patterned to form at least first, second and third electrodes 14 a, 14 b, 14 c separated by first and second trenches 16 a, 16 b. The silicon wafer 14 may be patterning using any one of many known methods in the wafer fabrication and processing arts for patterning silicon wafers, such as etching or micromachining. In the illustrative embodiment, the trenches 16 a, 16 b are etched down in the silicon wafer 14 to a depth which substantially exposes the dielectric substrate 12, e.g., silicon oxide.

At least a first nanowire 18 a may be formed in the first trench 16 a, which is operative to electrically couple the first electrode 14 a to the second electrode 14 b. Similarly, at least a second nanowire 18 b may be formed in the second trench 16 b, which is operative to electrically couple the second electrode 14 b to the third electrode 14 c. The formation of the first and second nanowires 18 a, 18 b in the respective first and second trenches 16 a, 16 b will be described below in further detail in connection with FIGS. 2 a through 2 f. It should be understood that the first nanowire 18 a may include a plurality of nanowires disposed in parallel to electrically couple the first and second electrodes 14 a, 14 b for which the greater the number of nanowires disposed between the first and second electrodes the greater the number of electrons that may be transported between the first and second electrodes 14 a, 14 b (i.e., increased current flow). It should also be understood and similar to that described above, the second nanowire 18 b may also include a plurality of nanowires disposed in parallel to electrically couple the second and third electrodes 14 b and 14 c for which the greater the number of nanowires disposed between the second and third electrodes 14 b, 14 c the greater the number of electrons that may be transported between the second and third electrodes 14 b, 14 c (i.e., increased current flow).

In an embodiment, the first and second nanowires 18 a, 18 b may include at least one of or a combination of silicon, carbon, gallium nitride, gallium arsenide, aluminum gallium arsenide, or related semiconductor alloys. In another embodiment, the first and second nanowires may include Ti- and Au-nucleated Si nanowires.

In the exemplary embodiment, at least the first and second nanowires 18 a, 18 b may be encapsulated in a first dielectric material 20, which serves to insulate and protect the first and second nanowires 18 a, 18 b and well as to provide a suitable platform to support respective first and second gate contacts 22 a, 24 a respectively disposed in close proximity to the first and second nanowires 18 a, 18 b. The insulated gate silicon nanowire transistor amplifier structure 10 further includes first drain and source contacts 22 b, 22 c which are respectively disposed on the first and second electrodes 14 a, 14 b. Similarly, the illustrated gate silicon nanowire transistor amplifier structure 10 also includes second drain and source contacts 24 b, 24 c, which are respectively disposed on the second and third electrodes 14 b, 14 c. In an embodiment, the first gate, drain and source contacts 22 a, 22 b, 22 c serve as an interface to a first transistor stage 22 of the transistor amplifier structure 10 and the second gate, drain, and source contacts 24 a, 24 b, 24 c serve as an interface to a second transistor stage 24 of the transistor amplifier structure 10. Further in the illustrative embodiment, the first source contact 22 c of the first transistor stage 22 and the second drain contact 24 b of the second transistor stage 24 are disposed in a contact relationship on the second electrode 14 b.

In an embodiment, the first drain contact 22 b of the first transistor stage 22 is adapted to receive current from a first power source 26, which may include a direct current source (e.g., a battery). The first gate contact 22 a may also be coupled to the first source contact 22 c, which first source contact 22 c is itself coupled to the second drain contact 24 b, as described above, to provide an output port 28 of the insulated gate silicon nanowire transistor amplifier structure 10 of the present invention. Further, the second gate contact 24 a may be adapted to receive an input voltage and/or control signals from a second power source 30 (e.g., alternating current source). Furthermore, the second source contact 24 c may be coupled to ground 32.

Referring to FIGS. 2 a through 2 d, shown is a method 100 for growing the first nanowire(s) 18 a associated with the first transistor stage 22 of the transistor amplifier structure 10 and it should be understood that the second nanowire(s) 18 b associated with the second stage 24 of the transistor amplifier structure 10 may be similarly formed. In particular, FIG. 2 a shows a thermal oxide layer 40 grown on a silicon wafer 42, which may be patterned to serve as an etch mask for the subsequent silicon wafer etching process. The mask edges should be carefully aligned along the intersections of the vertical planes with the top surface so that the subsequently etched first trench 16 a is bounded by two adjacent vertical surfaces 44 a, 44 b. The oxide may be etched using reactive ion etching (RIE) with CHF₃ and Ar gases, and the first trenches 16 a may be formed in the silicon wafer 14 by etching the silicon wafer in 44% KOH—H₂O at 110° C. for 1 min, which creates the first trench 16 a having dimensions of approximately 8 μm deep and 2-15 μm wide.

In FIG. 2 b, after forming the vertical surfaces 44 a, 44 b and cleaning the sample, a nucleating metal catalyst 46 of Ti or Au of the order of 1 nm thick may be deposited by electron-beam evaporation onto one of the vertical surfaces, such as surface 44 a of the etched trench 16 a. The vertical surface 44 a of the etched trench 16 a may be positioned at an angle of 45° from the normal to deposit the catalyst onto the vertical surface 44 a of the trench 16 a so that the nanowire(s) will grow preferentially from the vertical surface 44 a to the opposing vertical surface 44 b.

The structure 10 a may thereafter be transferred through air to a lamp-heated CVD reactor (not shown), in which the structure 10 a is supported by an SiC-coated graphite plate (not shown) of moderate thermal mass. The structure 10 a may be annealed in hydrogen at approximately 625 degrees Celsius to form Au—Si alloy nanoparticles and to reduce the native oxide on the Ti and form TiSi₂. The temperature may be increased to 625 degrees Celsius, and a mixture of SiH₄ and HCl may be introduced into the hydrogen ambient to grow the nanowire(s) 18 a, as shown in FIG. 2 c. The total pressure may be controlled at 10 Torr, with 3 slm of hydrogen, 15 sccm of SiH₄, and 15 sccm of HCl.

As shown in FIG. 2 d, the nanowire(s) 18 a may be grown for approximately 30 minutes or until the nanowire 18 a extends laterally towards and couples with the opposing vertical sidewall 44 b, which said another way forms a nanowire bridge across the trench 16 a. FIG. 2 e shows a scanning electron microscope image of one embodiment of the present invention in which the first trench 16 a includes the first nanowire 18 a as including a plurality of nanowires disposed to couple the first and second electrodes 14 a, 14 b. Similarly, FIG. 2 f shows another scanning electron microscope image of another embodiment of the present invention in which the first trench 16 a includes the first nanowire 18 a as including a unitary nanowire disposed to couple the first and second electrodes 14 a, 14 b

Referring to FIGS. 3 a and 3 b, after forming the first nanowire 18 a (i.e., which may includes one or more nanowires) in the first trench 16 a, which is electrically disposed to couple the first and second electrodes 14 a, 14 b, the method of the present invention includes encapsulating the first nanowire 18 a in a first dielectric material 48. In an embodiment, the first dielectric material 48 may include silicon dioxide or silicon nitride. In FIG. 3 c, after encapsulating the first nanowire 18 a in the first dielectric material 48, the method further includes substantially filling the remaining portions of the first trench 16 a with a second dielectric material 50. In an embodiment, the second dielectric material 50 may include silicon dioxide or silicon nitride. In FIG. 3 d, the first drain and first source contacts 22 b, 22 c may be formed on the respective first and second electrodes 14 a, 15 b using any one of a number of commonly known deposition processes. Finally, in FIG. 3 e, the first gate contact 22 a may be disposed on a portion of the first dielectric material 48, which operates to encapsulate the first nanowire 18 a, to form the first transistor stage 22 of the transistor amplifier structure 10. As mentioned above, it should be understood that the second transistor stage 24 of the transistor amplifier structure 10 may be similarly constructed and arranged as the first transistor stage 22. Further, in order to reduce processing steps and fabrication time, it should be understood that the second transistor stage 24 of the transistor amplifier structure 10 may be simultaneously fabricated as the first transistor stage 22 of the transistor amplifier structure 10.

Referring again to FIG. 1, during operation of the insulated gate silicon nanowire transistor amplifier structure 10 of the present invention, an input voltage is received at the second gate contact 24 a, which operates to generate an electric field between the second gate contact 24 a and the second nanowire 18 b for capacitively coupling the second gate contact 24 a and the second nanowire 18 b to permit electrons to flow through the second nanowire 18 b. This phenomena of electric field control of the second nanowire 18 b further permits current to be sourced from the first power source 26 (i.e., D.C. source) for providing a ballistic electon transport or current flow from the first power source 26 through the first drain contact 22 b; first electrode 14 a; first nanowire 18 a, second electrode 14 b; second nanowire 18 b, third electrode 14 c and out of the transistor amplifier structure 10 to ground 32, via the second source contact 24 c. At the same time, an amplified output voltage may be realized at the output part 28 of the transistor amplifier structure 10. In an embodiment, the output voltage is directly proportional to the magnitude of the current flowing through the transistor amplifier structure 10, as sourced by the first power source 26 and as described above. Since the magnitude of the current flowing through the transistor amplifier structure 10 is controlled by the magnitude of the input voltage received at the second gate electrode 24 a from the second power source 30, it logically follows that the output voltage realized at output port 28 is proportional to the magnitude if the input voltage signal received at the second gate contact 24 a.

It should be understood that the number of the first and second nanowires 18 a, 18 b can be increased to increase the number of parallel pathes, thereby increasing the current flowing at a given bias voltage through the transistor amplifier structure 10, which may translate into an increase in the amplified output voltage realized at the output port 28. It should also be understood that the transistor amplifier structure 10 of the present invention is fully scaleable and may be expanded to include additional transistor stages (not shown) without departing from the spirit and scope of the present invention.

One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety. 

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 5. A method of forming an insulated gate silicon nanowire transistor amplifier structure, comprising: (a) disposing a silicon layer on a dielectric substrate; (b) patterning the silicon layer for forming at least first, second and third electrodes separated by first and second trenches; (c) growing laterally at least a first nanowire in the first trench for electrically coupling the first and second electrodes; (d) growing laterally at least a second nanowire in the second trench for electrically coupling the second and third electrodes; (e) encapsulating the first and second nanowires in a first dielectric material; (f) disposing first drain and first source contacts on respective first and second electrodes; (g) disposing second drain and second source contacts on respective second and third electrodes; (h) disposing a first gate contact on the first dielectric material in close proximity to the first nanowire; and (i) disposing a second gate contact on the first dielectric material in close proximity to the second nanowire, wherein the first drain, source and gate contacts serve as an interface to a first transistor stage of the transistor amplifier structure and the second drain, source and gate contacts serve as an interface to a second transistor stage of the transistor amplifier structure.
 6. The method of claim 5, further including substantially filling the first and second trenches with a second dielectric material.
 7. The method of claim 6, wherein after the step (e), the method further includes removing a predetermined portion of the first dielectric material from the first, second and third electrodes to permit disposal of the first and second drain and source contacts.
 8. The method of claim 7, further including coupling the first gate, first source and second drain contacts for defining an output.
 9. The method of claim 8, further including coupling the first drain contact to receive input current from a first source.
 10. The method of claim 9, further including coupling the second gate contact to receive input current from a second source, wherein input current from the second source induces an electric field between the second gate contact and the second nanowire to permit current from the first source to flow through at least the first and second nanowires for providing a proportional voltage at the output. 